The present invention relates to orthodontic appliances for correcting misalignments of a patient's teeth. More particularly, the present invention relates to an orthodontic arch wire which can be used together with a series of orthodontic brackets in order to provide efficient and effective correction of a variety of classes of malocclusions.
A variety of malocclusions can be corrected through the use of orthodontic arch wires. In corrections using arch wires, brackets are secured to the patient's teeth by the use of bands to which the brackets are welded, or by cementing brackets directly to the teeth. Typically, in each of a number of stages during the course of treatment, an arch wire is secured in the brackets. As treatment progresses, the arch wire which is used more closely approaches the ideal arch form. The arch wires progressively correct misalignments of the patient's teeth.
Malocclusions have conventionally been corrected through what is known in the art as edgewise or light wire techniques. In the edgewise technique, which is utilized to avoid the problem of "tipping" and to prevent the teeth from acquiring a "dished" appearance, orthodontic brackets having open rectangular slots are secured to the patient's teeth, and an orthodontic arch wire having a rectangular cross-section is inserted into the rectangular slots so that such slots support the arch wire. Since the arch wire cannot rotate in the rectangular slots of the brackets, and since the brackets are fixed to the incisors, rearwardly applied forces on the arch wire are prevented from causing "tipping" of the incisors. The non-rotating relationship between the rectangular arch wire and the bracket is such that torque can be applied to the teeth by the arch wire through the brackets when required.
As indicated in U.S. Pat. No. 4,424,033, incorporated herein by reference in its entirety, one problem with the edgewise technique is that the rectangular arch wire tends to bind in the brackets secured to the posterior teeth as a result of excessive friction, and in some cases, the friction between the arch wire and the posterior tooth brackets interferes with the action of the arch wire in correcting anterior tooth protrusions. As a solution to this problem, U.S. Pat. No. 4,424,033 discloses an orthodontic arch wire provided with posterior segments which each have a circular cross-section and an anterior segment which has a uniform non-circular cross-section substantially throughout its entire length. Because the circular posterior segments of the arch wire have a lesser tendency to bind in the posterior brackets, there is a reduced likelihood that friction between the posterior tooth brackets and the arch wire will interfere with the application of a rearward force to the anterior teeth. Furthermore, the non-circular cross-section of the anterior segment of the arch wire cooperates with the slots in the anterior brackets to ensure rearward translation of the anterior teeth rather than tipping.
U.S. Pat. No. 4,424,033 also discloses an improvement of the arch wire associated with the solution above wherein rather than using a rectangular arch wire, an arch wire having a tapered, symmetrical, trapezoidal cross-section in its anterior segment is utilized. (It should be noted that for the purposes of this application, the term symmetrical trapezoidal cross-section will be used to refer to trapezoidal cross-sections in which neither the upper nor the lower surfaces thereof are perpendicular or substantially perpendicular to the vertical surfaces of the trapezoidal cross-section. Likewise, the term symmetrical trapezoidal arch wire will be used to refer to orthodontic arch wires of which at least a portion thereof has a symmetrical trapezoidal cross-section as defined above). The tapered anterior segment of the arch wire cooperates with correspondingly tapered edgewise slots in the anterior tooth brackets. Also, the tapered anterior segment and tapered slots slide together easily but provide a tight enough fit so that torque can be applied through the arch wire to the brackets. Furthermore, the tapered anterior segment and tapered slot eliminate the need for extremely close manufacturing tolerances.
Although the trapezoidal arch wires described in U.S. Pat. No. 4,424,033 overcome some of the more notable problems associated with the use of rectangular arch wires, it is likely that some orthodontists, especially those who have been practicing for a significant number of years, will refrain from using the symmetrical trapezoidal arch wires because such arch wires have a noticeably different configuration from the standard rectangular arch wires to which they have been accustomed. More particularly, since many orthodontists are accustomed to using rectangular arch wires as means for correcting malocclusions, such orthodontists may be unwilling to try the improved symmetrical trapezoidal arch wires.
Furthermore, since many existing orthodontic brackets are of the type having rectangular arch wires slots, some orthodontists may be willing to continue using the rectangular arch wires rather than the symmetrical trapezoidal arch wires, even though they are aware of the advantages of the symmetrical trapezoidal arch wires, in situations where they have a surplus of rectangular-slot brackets in their possession, or where their patients have already been outfitted with a series of rectangular-slot brackets.